1. Field of the Invention
The present invention relates to an optical compensator element, in which the level of phase difference is variable by the application of voltage, and a liquid crystal display using the same.
2. Background Art
Liquid crystal displays (hereinafter referred to as “LCDs”) have features of thin, lightweight, low power consumption, and freedom from flicker. For this reason, LCDs are extensively used in various displays, that is, large stationary displays, as well as displays of portable terminal equipment and the like.
In the case of portable terminal equipment, what is sometimes required of displays is that display can be seen only by the user while the display cannot be seen by a person(s) around the user. On the other hand, in some cases, display should be positively seen by a person(s) around the display. These are true of large and stationary displays.
In recent years, spread of digital still cameras, an improvement in communication infrastructure and the like have led to ever-increasing cases where photographs and motion images are displayed on a display of portable terminal equipment. A typical example thereof is a portable (cellular) phone. In displaying photographs or the like on the display screen of the portable phone, when it is desired that a plurality of observers around the display can see the display, the angle of visibility of the display is desired to be satisfactorily wide. For example, in LCDs, the angle of visibility can be increased by applying a phase difference film to a liquid crystal cell. In the case of transmission and receipt of electronic mails (E-mails) or the like, it is preferred that the display can be seen only by the sender or receiver and cannot be seen by persons, other than the sender or the receiver, around the display. In this case, the angle of visibility of the display screen should be reduced.
Accordingly, display which can realize switching between a wide angle of visibility and a narrow angle of visibility through a simple operation has been desired.
The angle of visibility of LCD per se is intrinsically narrow. The reason for this is that increasing the angle of visibility causes leakage of light from pixels which should display black, resulting in a change in color tone or tone reversal or the like. In order to increase the angle of visibility, a reduction in leakage of light from pixels, which should display black, in all the direction of angle of visibility is effective.
An optical compensation film formed of an optically anisotropic transparent film has been widely utilized as means for increasing the angle of visibility of LCDs. This optical compensation film can be prepared, for example, by monoaxially or biaxially stretching a transparent resin film, for example, polycarbonate, polyethylene terephthalate, or polyolefin such as polyethylene. Further, in recent years, an optical compensation film utilizing a liquid crystal layer which can be fixed while maintaining the liquid crystal phase has also been reported. In use, in general, these optical compensation films are applied to a polarizing plate, followed by application to a liquid crystal cell.
Modes of LCDs include twisted nematic (hereinafter abbreviated to TN) mode, homeotropic alignment or vertical alignment (hereinafter abbreviated to VA) mode, in plane switching (hereinafter abbreviated to IPS) mode, and optically compensated bend (hereinafter abbreviated to OCB) mode. Among them, discotic liquid crystal or nematic liquid crystal, which has been fixed by hybrid alignment, is used as the optical compensation film for TN-mode LCDs, a combination of a positive A plate with a negative C plate is used as the optical compensation film for VA-mode LCDs, and a combination of a positive A plate with a positive C plate is used as the optical compensation film for IPS-mode LCDs, and a biaxially stretched transparent resin film is used as the optical compensation film for OCB-mode LCDS.
In a construction in which an optical compensation film (a phase difference film) for realizing a wide angle of visibility is applied and fixed to a display, however, when realization of a narrow angle of visibility is contemplated, the optical compensation film should be separated, and, consequently, switching between a wide angle of visibility and a narrow angle of visibility could not be carried out through a simple operation.